1. Field of the Invention
The subject disclosure relates to a control system for use with aircraft gas turbine engines, and more particularly to, a control system which includes a “real-time” Time Limited Dispatch fault management system which evaluates engine electronic component failures and determines the allowable engine operational running time with failures present in the control system based on predicted component failure rates.
2. Background of the Related Art
Often aircraft engine control systems have redundant components or elements to improve flight safety or for increasing the operational running time between maintenance periods. In engine control systems which have redundant components or elements, Time Limited Dispatch (TLD) methodologies are applied to evaluate whether an engine can continue to operate for a predetermined length of time with faults present in the redundant components/elements, before repairs are required. More specifically, the TLD methodologies are a means for substantiating and obtaining approval for dispatching and operating a Full Authority Digital Engine Control (FADEC) equipped aircraft, for limited time periods, with faults present in the system, after which, appropriate repairs shall be made to bring the system to the “full up” configuration. The term “full up” is used to indicate that the FADEC system is free of faults which affect the loss of thrust control (LOTC) failure rate.
The FADEC system controls the operation of the engine over an entire performance range, usually from engine start-up to maximum power or thrust. The FADEC system consists generally of an electronic engine control (EEC) unit, a fuel metering unit (i.e. hydromechanical control unit), sensors, actuators, valves, an alternator and interconnecting electrical harnesses. FIG. 1b provides a schematic representation of a typical FADEC system for a dual channel EEC unit.
In multiengine aircraft, TLD methodologies are applied independently to each engine when determining the allowable operating time (i.e., dispatch service time). Thus the aircraft could be dispatched with faults present in more than one engine's FADEC system.
SAE, the engineering society for advancing mobility on land, sea, air and space, publishes aerospace recommended practice (ARP) 5107 which provides methodologies and approaches which are presently used for conducting and documenting the analysis associated with the application of TLD to FADEC systems. Traditionally, under the SAE approach, maintenance or dispatch crews are required to perform a multitude of calculations on the ground to determine if the aircraft can be dispatched for a particular mission. This approach is performed while the aircraft is on the ground, is often very time consuming, and results in a less than optimal maintenance schedule.
There is a need therefore, for a fault management system which is integrated with the aircraft's control system and is capable of analyzing fault scenarios in “real-time” so as to assist pilots or maintenance personnel in making intelligent decisions on the dispatch capability of the aircraft.